Identification and Purification of a Toxic Component to B Cell Hybridoma Cells in Fetal Calf Serum

A component exhibiting toxicity to B cell hybridoma cells was isolated and purified from fetal calf serum (FCS) by immunoaffinity chromatography using a monoclonal antibody (mAb) which reacted with the high‐molecular‐weight glycoprotein (6B3·Ag) recognized by a mAb, 6B3, to human large cell lung carcinoma cells (HLC‐2). The component (FCS‐6B3·Ag) was a high‐molecular‐weight antigen (approximately 1,000,000), consisting mainly of 76,000 subunits. FCS‐6B3·Ag showed the same mobility in the pre‐β globulin region as that of 6B3·Ag on electrophoresis in 1.2% agarose gel. When FCS‐6B3·Ag was analyzed by double immunodiffusion, it reacted with anti‐6B3·Ag antiserum and the precipitin line fused partially with that formed between 6B3·Ag and anti‐6B3·Ag antiserum. FCS‐6B3·Ag was found to be toxic to hybridoma cells (anti‐6B3·Ag, anti‐α‐fetoprotein, anti‐carcinoembryonic antigen or anti‐C‐reactive protein mAb producing cells) specifically in vitro at 5 μg/ml. The antigen also strongly suppressed their growth. The toxic effect of FCS‐6B3·Ag appeared immediately after addition, and death of the target cells was complete only after 36–48 h. However, the antigen exhibited only weak suppression of Ig‐non‐secretory mouse myeloma (P3U1), thymic lymphoma (EL4) or mastocytoma (P815) cell growth. Five lots of FCS contained 2.1 to 4.1 μg/ml of FCS‐6B3·Ag.